A method and an arrangement for controlling the speed of a vehicle are discloses in German patent publication 2,924,391. Here, a power adjusting element of the drive unit of the motor vehicle is adjusted, on the one hand, via the accelerator pedal actuation of a driver and, on the other hand, via the limiting controller operating on the basis of the difference between the actual speed and the limit speed. The adjustment of the power adjusting element is dependent upon the position of the accelerator pedal as long as the limit speed is not reached. If the driver actuates the accelerator pedal in such a manner that the limit speed is exceeded, then the power adjusting element is adjusted by the limit controller in the sense of maintaining the limit speed. If, in this operating state, the driver takes his foot from the accelerator pedal, then the power adjusting element is closed because the setting of the power adjusting element is dependent upon the position of the accelerator pedal.
The speed controller continues to run in the known state of the art. The output signal of the controller becomes very large as a consequence of the occurring control difference between the desired and actual speeds, that is, the output signal would drive the power adjusting element in the sense of higher power. If the driver again depresses the accelerator pedal in this driving state so that the speed again exceeds the limit speed, then high overshoots can be expected because of the start value of the speed controller which is too high.
A procedure known in the control art for avoiding such unwanted situations is to maintain the last controller value which occurs when moving out of the control range. This retained controller value then serves as a start value for a new entry into the control region. Driving uphill with subsequent depression of the accelerator pedal leads to the situation that the start value of the controller is too low and it therefore takes a long time until the desired speed is again reached.
U.S. patent application Ser. No. 08/652,582, filed Jun. 7, 1996, (corresponding to PCT patent publication WO 95/15868) discloses a road speed limiter wherein a desired acceleration of the vehicle is determined on the basis of the difference between desired speed and actual speed. A controller controls to this desired acceleration while considering the actual acceleration of the vehicle. The desired acceleration when reaching the desired speed is 0. In a controller concept of this kind, the driver can drive the power adjusting element in the sense of a power reduction when releasing the accelerator pedal. For this reason, corresponding problems occur.
A corresponding problematic results for speed controllers which are inhibited by the driver by actuating the accelerator pedal and are again enabled automatically when the driver releases the accelerator pedal. In this connection, reference can be made, for example, to German patent publication 4,038,432.